This invention relates to the use of a natural-based starch material as a sunscreen agent in aqueous sunscreen compositions.
The harmful effects from excessive exposure of human skin to ultraviolet radiation from the sun and other sources is well known. The need to protect human skin from ultraviolet radiation, particularly solar radiation, has been well documented in recent years and a variety of sunscreen preparations have been developed to provide varying degrees of screening or blocking protection.
Sunscreens are of two types, physical and chemical. Physical screening agents, such as titanium dioxide and zinc oxide, are opaque materials that block and scatter light and therefore act as mechanical barriers. Chemical screening agents act by absorbing ultraviolet light and offer selective protection against certain ultraviolet wave bands depending on their absorption spectrum. Anthranilates, cinnamates, benzyl and homomenthyl salicylate and aminobenzoic acid and its ester derivatives are absorbing sunscreen agents of this type.
Sunscreen compositions are generally available in various forms such as creams, lotions and oils containing the active sunscreen agent disposed in a pharmaceutically acceptable carrier. Illustrative compositions are shown in U.S. Pat. No. 4,917,883 which discloses an oil-in-water emulsion sunscreen composition containing selected film formers and sunscreen agents such as aminobenzoate esters; U.S. Pat. No. 5,026,540 which discloses a clear, waterproof sunscreen composition comprising a film forming vinylpyrrolidone copolymer, a sunscreening agent and an emollient; and U.S. Pat. Nos. 4,401,649 and 4,935,533 which disclose sunscreen compositions containing respectively selected aminobenzoate esters of alkylene diols or polyols and 1-cyclohexenylacetonitrile derivatives as sunscreen agents. U.S. Pat. No. 4,894,222 discloses a waterproof sunscreen formulation comprising a mixture of an aliphatic wax and anhydrous hydrophobic starch as its waterproofing agents in a water-free carrier containing one or more conventional Uv absorbers as the sunscreen agent.
For topical applications to the skin, sunscreen compositions must be nontoxic and non-irritating to the skin tissue and capable of application as a continuous film. In addition, the active sunscreening agent must be chemically stable and in particular must be resistant to chemical and photodegradation when on the skin as well as resistant to absorption through the skin.